Hi @~OSD~
Try a minimum length of 6 digits.
With this policy setting, you can configure a minimum length for a TPM startup PIN. This policy setting is applied when you turn on BitLocker. The startup PIN must have a minimum length of four digits, and it can have a maximum length of 20 digits. By default, the minimum PIN length is 6.
Configure minimum PIN length for startup
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If this is helpful please accept answer.